The disclosure of Japanese Patent Application No. 2001-292927 filed on Sep. 26, 2001 including the specification drawings, and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a control system and a control method for an in-cylinder injection type internal combustion engine.
2. Description of Related Art
In an in-cylinder injection type internal combustion engine used in an automobile, a large quantity of fuel is injected at the time of engine startup, due to the fact that some of the fuel that is injected adheres to the inside wall surface of the combustion chamber, the demanded fuel injection quantity is increased by a corresponding amount.
Thereafter, when the fuel adhered to the inside wall surface of the combustion chamber begins to vaporize, the demanded fuel injection quantity that has been increased at engine startup by the amount of fuel that vaporizes is decreased. Because the vaporization rate of the adhered fuel increases as the temperature of the combustion chamber rises, the fuel injection quantity can be reduced such that the fuel injection quantity decreases the higher the temperature of the combustion chamber, as is disclosed in Japanese Patent Application Laid-Open Publication No. 11-270386, for example.
When the engine is stopped when the temperature of the combustion chamber is still low after beginning to start the engine from a cold state, and then restarted immediately thereafter, a large amount of fuel, as described above, is injected because the temperature of the combustion chamber is low. This means that a large amount of fuel is injected even though the fuel injected when the engine was started the last time is adhered to the inside wall surface of the combustion chamber. As a result, the air-fuel ratio of the mixture in the combustion chamber may become rich thus leading to poor combustion of the mixture.
In view of the foregoing problem, it is an object of the invention to provide a control system or a control method for an in-cylinder injection type internal combustion engine that can prevent the air-fuel ratio of the mixture in the combustion chamber from becoming excessively rich when the engine is restarted when the temperature of the combustion chamber at the beginning of engine stop of the most recent engine operation is low, and therefore minimize the possibility of poor combustion of that mixture resulting from an excessively rich air-fuel mixture.
In order to achieve the foregoing object, according to a first aspect of the invention, a control system for an in-cylinder injection type internal combustion engine is provided with a controller that estimates the temperature of a combustion chamber at the beginning of engine stop of the most recent engine operation when there is a command to start the engine, and that corrects the air-fuel ratio of the mixture supplied to the combustion chamber at engine startup to the lean side based on the estimated temperature of the combustion chamber.
When the temperature of the combustion chamber is low at the beginning of engine stop of the most recent engine operation, it is highly likely that fuel is already adhered to the inside wall surface of the combustion chamber when the engine is restarted. According to this first aspect of the invention, it is possible to mitigate the air-fuel ratio of the mixture within the combustion chamber from becoming excessively rich, and therefore minimize the possibility of poor combustion of that mixture resulting from an excessively rich air-fuel mixture under these conditions by correcting the air-fuel ratio of the mixture to the lean side.
Moreover, the controller may also correct the air-fuel ratio to the lean side by reducing the fuel injection quantity at engine startup based on the estimated temperature of the combustion chamber. In particular, because it is highly likely that fuel is already adhered to the inside wall surface of the combustion chamber when the engine is restarted when the estimated temperature of the combustion chamber is low, reducing the fuel injection quantity at engine startup can prevent the air-fuel ratio of the mixture inside the combustion chamber from becoming excessively rich, and therefore minimize the possibility of poor combustion of that mixture resulting from an excessively rich air-fuel mixture.
Further, the controller may also reduce the fuel injection quantity at engine startup when the amount of time from the most recent engine operation until engine startup is short.
For a short interval between the most recent engine operation and the engine restart is short, the fuel adhered to the inside wall surface of the combustion chamber has insufficient time to completely vaporized. As a result, it is highly likely that fuel is already adhered to the inside wall surface of the combustion chamber when the engine is restarted. By reducing the fuel injection quantity at engine startup when only a short amount of time has passed after the most recent engine operation, it is possible to minimize the possibility of the fuel injection quantity being reduced unnecessarily.
Moreover, the air-fuel ratio may also be corrected to the lean side by increasing the intake air quantity based on the estimated temperature of the combustion chamber. In particular, because it is highly likely that fuel is already adhered to the inside wall surface of the combustion chamber upon engine restart when the estimated temperature of the combustion chamber is low, increasing the intake air quantity at engine startup can avoid excessively rich air-fuel ratio of the mixture inside the combustion chamber, and therefore minimize the possibility of poor combustion of that mixture resulting from an excessively rich air-fuel mixture.
Further, the controller may also increase the intake air quantity at engine startup when the amount of time from the most recent engine operation until engine startup is short.
For a short interval between the most recent engine operation and the engine restart, the fuel adhered to the inside wall surface of the combustion chamber is not able to be completely vaporized during that time. As a result, it is highly likely that fuel is already adhered to the inside wall surface of the combustion chamber when the engine is restarted. By increasing the intake air quantity at engine startup when only a short amount of time has passed after the most recent engine operation, it is possible to minimize the possibility of the fuel injection quantity being reduced unnecessarily.
Also, the temperature of the combustion chamber at the beginning of engine stop may also be estimated based on at least the engine cooling water temperature at the beginning of engine stop of the most recent engine operation.
When the cooling water temperature is low at the beginning of engine stop, the temperature of the combustion chamber is also low at the beginning of engine stop. Therefore, by estimating the temperature of the combustion chamber based on the engine cooling water temperature when the engine was stopped the last time, it is possible to accurately estimate the temperature of the combustion chamber at the beginning of engine stop.
Also, according to a control method for an in-cylinder injection type internal combustion engine, in a second aspect of the invention, the temperature of the combustion chamber at the beginning of engine startup of the most recent engine operation is estimated when there is a command to start the engine. The air-fuel ratio of the mixture to be supplied to the combustion chamber at engine startup is corrected to the lean side based on the estimated temperature of the combustion chamber.
When the temperature of the combustion chamber is low at the beginning of engine stop of the most recent engine operation, it is highly likely that fuel is already adhered to the inside wall surface of the combustion chamber when the engine is restarted. According to this second aspect of the invention, it is possible to mitigate the air-fuel ratio of mixture within the combustion chamber from becoming excessively rich, and thereby minimize the possibility of poor combustion of that mixture resulting from an excessively rich air-fuel mixture under these conditions by correcting the air-fuel ratio of the mixture to the lean side.